Make resize/migrated shared storage aware

Fixes bug 1177247

Added some logic to check for whether or not we are on a shared
filesystem and set shared_storage accordingly. We perform similar
checks in other areas of the code, typically through RPC calls.
However, all the resize/migrate code is slated to be refactored for
Hava, so the idea was to keep this patch as minimally intrusive as
possible.

When shared_storage is true, we pass that on to the cleanup call
so that it no longer executes an rm via SSH, which was ultimately
destroying the original instance directory.

Change-Id: Ie9decedd373c000211c171df64e1e96fe78e5081
Merge "Make resize/migrated shared storage aware"